Atomic Theory Flashcards
Define radioactivity.
Radioactivity is the spontaneous breaking up of an unstable nucleas with the emission of one or more types of radiation.
Explain Heisenberg’s uncertainty principle.
The more closely you are to knowing the position of an electron the further you are from knowing it’s velocity.
Electronegativity down a group.
~Shielding effect
~Bigger atomic radius
Electronegativity across a group
~Increases
~Increase in nuclear charge
~Smaller atomic radius
Define half life.
Time taken for half of the nuclei in a sample to decay.
What’s atomic mass?
Number of protons in the nucleas of an atom.
The trend in electronegativity values down the first group of elements.
EN vales decrease down group because of shielding effect.
Define orbitals
Region in the space around the nucleas of an atom which electrons are most likely to be found.
Relative atomic mass
The average mass of an element as it occurs in nature compared to 1/12 of the mass of a 12 carbon isotope.
What is electronegativity?
Measure of attractiveness an atom has for a shared pair of electrons in a covalent bond.
What is the first ionisation energy?
Minimum energy required to remove the most loosely bound electron form an atom in its ground state.
What is molar mass?
The mass in grams of a mole of that substance.
What is atomic radius ?
Half the distance between the nuclei of two singly covalenty bonded atoms./ of two identical atoms joined by a single covalent bond
What is mass number?
Number of protons+ neutrons
Define isotopes
Atoms of the same element which have same number of protons but different numbers of neutrons.
What was the purpose of Milikan’s oil drop experiment?
To determine the charge of an electron
Name the scientist who identified cathode rays as a subatomic particle and also measure the charge to mass ratio?
J. J. Thompson
Describe Thompson’s “plum pudding”
model of the atom which had negatively-charged electrons embedded within a positively-charged “soup”/ sphere
Rutherford used alpha particles. What are these?
Helium nucleus. Two protons and two neutrons
2 properties of cathode rays
Travel in straight lines/ negligible mass/ negatively charged
State two assumptions of Dalton’s atomic theory of 1808
Atoms are small and indivisible
Who measured the charge of the electron?
Millikan
Who measured the ratio of charge to mass of an electron
J. J. Thompson
What did Rutherford do?
Proved that electrons in an atom reside in an electron cloud surrounding a small dense positive nucleus
Law of conservation of mass
When a chemical reaction takes place, matter is neither created or destroyed but merely changes from one form to another.
Matter
Anything that occupies space and has mass.
Relative molecular mass
Sum of relative atomic masses of all atoms in a molecule of the compound compared to 1/12 of the mass of a carbon-12 isotope
Three fundamental processes that occurred in the mass spectrometer
Ionisation/ acceleration/ separation
What result did Rutherford expect to get when thin gold foil was bombarded with alpha particles?
Alpha particles were expected to pass straight through/ Un deflected
How did the actual result of Rutherford’s experiment differ from the expected result
Some particles were deflected at large angles /nuclease positive / almost all passed through/ some bounced straight back
How was the model of atomic changed as a result of Rutherford’s experiment
Large electron cloud surrounding/ atoms mostly empty space/ nuclease very small
Energy level
Shell which electrons of equal energy can occupy
Aufbau principle
Electrons occupy the lowest available energy level
What was Dalton’s atomic theory
Matter composed of atoms/ atoms are tiny particles/ atoms are indivisible/ cannot be created or destroyed
What happens in a radioactive nuclease during beta decay?
Neutron changes into proton and an electron which is emitted
How did Mendeleev arrange the elements in the periodic table of 1869?
According to atomic weight/ in groups of similarities properties
How do we know that any new element discovered in the future will be super heavy
No gaps in modern periodic table/ all other lighter elements known
Main energy levels in electron transition that gives rise to the first line of the balmer series in the emission spectrum of the hydrogen atom
3 and 2
Describe trend in covalent radii for atoms of the second period of the periodic table
Increases because of additional shells/ increase in nuclear charge
Term used for the condition of the hydrogen atom when its electron occupies any of the levels E2,E3,etc?
Excited state
What causes the electron to leave the E1 level?
Acquires energy /heat
Why does the electron not remain in any of the levels E2,E3,etc?
Higher energy states unstable
How does modern atomic theory describe the behaviour of electrons?
Electrons have both wave and particle properties
Cathode rays
Beams of electrons/ negatively charged
Advantage of arranging elements in order of atomic number
Indicates gaps/ undiscovered elements / tellurium and iodine positions are justified
Position of tellurium and iodine in the 1869 table
Listed according to chemical properties/ listing by atomic mass wouldn’t group them with elements of the similar properties
Periodic system in context of Mendeleev’s 1869 table
Elements listed according to atomic mass/ properties repeat periodically
Why the elements of group 18 in the table are chemically inert
Stable arrangement of electrons/ do not lose or gain electrons
Scientist who discovered presence of cathode rays
Crookes( paddle wheel experiments)
Who discovered the neutron?
Chadwick
Give a reason for the general increase in first ionisation energy across a period of the periodic table
the increase in nuclear charge having a greater pull on the electrons and therefore more energy is required to remove electrons
Explain why the general increase in first IE is interuppted
The repulsion between 2 electrons makes one of them easier to remove/ beacuse boron has a smaller value than baylium
Mass spectrometer processes
- Vaporitasion
- Ionisation
- Acceleration
- Seperation
- Detection
- Display
Describe ionisation process in mass spectrometer
The sample is ionised by bombarding it with high energy electrons
Describe acceleration and sepearation in mass soectrometer (process 3&4)
Acceleartion: positive ions are accelerated by negatively charged plates.
Seperation: ions are deflected by magnetic feild
What is the last process in mass spectometer
Detection: ions are detected by a sensitive plate
What are gamma particles?
Electromagnetic radiation. Highly penetrating
